CloudWatch: Update Period `auto` to take retention into account (#37424)

* now to get it to build

* modified names, added the 455 day case, and added a comment

* removed wireguard override i used for my local

* updated the docs

docs/sources/datasources/cloudwatch.md

@@ -180,7 +180,7 @@ Please note that in the case you use the expression field to reference another q
 
 A period is the length of time associated with a specific Amazon CloudWatch statistic. Periods are defined in numbers of seconds, and valid values for period are 1, 5, 10, 30, or any multiple of 60.
 
-If the period field is left blank or set to `auto`, then it calculates automatically based on the time range. The formula used is `time range in seconds / 2000`, and then it snaps to the next higher value in an array of predefined periods `[60, 300, 900, 3600, 21600, 86400]`. By clicking `Show Query Preview` in the query editor, you can see what period Grafana used.
+If the period field is left blank or set to `auto`, then it calculates automatically based on the time range and [cloudwatch's retention policy](https://aws.amazon.com/about-aws/whats-new/2016/11/cloudwatch-extends-metrics-retention-and-new-user-interface/). The formula used is `time range in seconds / 2000`, and then it snaps to the next higher value in an array of predefined periods `[60, 300, 900, 3600, 21600, 86400]` after removing periods based on retention. By clicking `Show Query Preview` in the query editor, you can see what period Grafana used.
 
 ### Deep linking from Grafana panels to the CloudWatch console
 

pkg/tsdb/cloudwatch/request_parser.go

@@ -69,7 +69,7 @@ func parseRequestQuery(model *simplejson.Json, refId string, startTime time.Time
 	var period int
 	if strings.ToLower(p) == "auto" || p == "" {
 		deltaInSeconds := endTime.Sub(startTime).Seconds()
-		periods := []int{60, 300, 900, 3600, 21600, 86400}
+		periods := getRetainedPeriods(time.Since(startTime))
 		datapoints := int(math.Ceil(deltaInSeconds / 2000))
 		period = periods[len(periods)-1]
 		for _, value := range periods {
@@ -123,6 +123,19 @@ func parseRequestQuery(model *simplejson.Json, refId string, startTime time.Time
 	}, nil
 }
 
+func getRetainedPeriods(timeSince time.Duration) []int {
+	// See https://aws.amazon.com/about-aws/whats-new/2016/11/cloudwatch-extends-metrics-retention-and-new-user-interface/
+	if timeSince > time.Duration(455)*24*time.Hour {
+		return []int{21600, 86400}
+	} else if timeSince > time.Duration(63)*24*time.Hour {
+		return []int{3600, 21600, 86400}
+	} else if timeSince > time.Duration(15)*24*time.Hour {
+		return []int{300, 900, 3600, 21600, 86400}
+	} else {
+		return []int{60, 300, 900, 3600, 21600, 86400}
+	}
+}
+
 func parseStatistics(model *simplejson.Json) []string {
 	var statistics []string
 	for _, s := range model.Get("statistics").MustArray() {

pkg/tsdb/cloudwatch/request_parser_test.go

@@ -208,5 +208,32 @@ func TestRequestParser(t *testing.T) {
 			require.NoError(t, err)
 			assert.Equal(t, 86400, res.Period)
 		})
+
+		t.Run("Time range is 2 days, but 16 days ago", func(t *testing.T) {
+			query.Set("period", "auto")
+			to := time.Now().AddDate(0, 0, -14)
+			from := to.AddDate(0, 0, -2)
+			res, err := parseRequestQuery(query, "ref1", from, to)
+			require.NoError(t, err)
+			assert.Equal(t, 300, res.Period)
+		})
+
+		t.Run("Time range is 2 days, but 90 days ago", func(t *testing.T) {
+			query.Set("period", "auto")
+			to := time.Now().AddDate(0, 0, -88)
+			from := to.AddDate(0, 0, -2)
+			res, err := parseRequestQuery(query, "ref1", from, to)
+			require.NoError(t, err)
+			assert.Equal(t, 3600, res.Period)
+		})
+
+		t.Run("Time range is 2 days, but 456 days ago", func(t *testing.T) {
+			query.Set("period", "auto")
+			to := time.Now().AddDate(0, 0, -454)
+			from := to.AddDate(0, 0, -2)
+			res, err := parseRequestQuery(query, "ref1", from, to)
+			require.NoError(t, err)
+			assert.Equal(t, 21600, res.Period)
+		})
 	})
 }